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Structure and dynamica of crystalline nano-systems

Abstract: X-ray research is facing a new era with the advent of the free electron lasers (FELs). The first experiments are being conducted at LCLS in California while the European XFEL and Japanese compact SASE source are both under construction. The x-ray bunches of the FELs have a time resolution on the order of 100fs and can be focused to hundreds of nanometer, properties which naturally lends the FELs to both time-resolved pump-probe experiments, studies on the nanoscale and combinations thereof.

Within the field of x-ray diffraction both types of experiments have been the subject of the thesis work presented here. In the first experiments we used surface x-ray diffraction techniques and reciprocal space mapping to study the structure and growth of semiconductor nanowires. The second type of diffraction experiments are time-resolved laser pump x-ray probe experiments performed at the FEMTO beamline of SLS. We studied the electronic deformation in metals by measuring and modelling laser induced strain waves in Au and found a weak electronic contribution to the expansion. In addition we studied the structural part of the anti-ferromagnetic to ferromagnetic phase transition in FeRh. Finally the two main subjects are combined in a time-resolved x-ray study of laser excited acoustic oscillations in InAs nanowires. We measured both the absolute motion of the wires as well as the period of the oscillations, and are thus able to test the predictions made by classical continuum elasticity theory.

In this talk I will give a brief explanation of the diffraction principles for reciprocal space mapping derived and applied in all of this work, but otherwise focus on the time-resolved x-ray studies on metals and nanowires.